1. Field of the Invention:
The present invention relates to a rotor for a "printed-wiring" motor in which the conductors consist of printed-wiring strips on each side of a thin insulating disc.
2. Prior Art:
In general, conventional printed-wiring motors include a flat rotor or armature composed of a pair of sheet coil assemblies joined together with a thin insulating disc between the sheet coil assemblies. Each sheet coil assembly consists of a pair of sheet coils joined together with a thin insulating disc between the two sheet coils. The insulating disc is composed of sheet mica coated with a thermosetting resin. These mica insulating discs are expensive; and in view of this drawback, relatively inexpensive insulations have been proposed, for example, as shown in Japanese Utility Model Laid-open Publication No. 53-18501. The proposed inexpensive insulating disc is composed of a fabric sheet of glass-wool impregnated with a thermosetting insulating resin.
The known insulating discs are found disadvantageous for the reasons described below. The mica is not only expensive but also is likely to crack or otherwise become broken, because it is characterized by low hardness and perfect basal cleavage. This means that the mica insulating disc must be handled carefully; otherwise, an insulation failure could be caused by the cracked or broken mica insulation disc. Furthermore, the mica generally contains a certain amount of impurities (so-called "red spots") which lower the insulation characteristics of the mica insulation disc. Another drawback associated with the mica insulation disc is that a substantial reduction in bonding strength of the thermosetting insulating resin is likely to occur due to the cleavage of the mica.
The resin-impregnated fabric sheet of glass-wool (the so-called "prepreg" sheet) disclosed in Japanese Utility Model Laid-open Publication 53-18501 has a relatively larger thickness because of a certain lower limit to the diameter of glass fibers. With this larger the thickness, the prepreg sheet lowers the motor efficiency.
The sheet coil is generally formed by stamping a sheet of copper into a predetermined wiring pattern, during which time, burrs are produced on the underside of the stamped sheet coil. When two such stamped sheet coils are joined together in back-to-back confrontation with a thin mica insulating disc disposed therebetween, the burrs bite into the mica and sometimes contact the burrs on the opposite sheet coil, thereby causing a short-circuiting or insulation failure. Since the insulation failure can be found only when the continuity of a rotor is checked, the occurrence of an insulation failure of a sheet coil assembly means discarding a rotor assembly in which the defective sheet coil is used. This insulation failure does not occur when a relatively thick prepreg sheet of glass-wool is used. However, a high motor efficiency is difficult to obtain using the thick prepreg sheet.